Corrosion protection of metals



Patented 13, 1945 CORROSION PROTECTION OF METALS Ernest W. Zulilin,Sausalito, Emmett R. Barnum,

Berkeley, and Ellis R. White, Albany, Calif., assignors to ShellDevelopment Company, San Francisco, Calif., a corporation of Delaware NoDrawing.

The present invention relates to metals or metal-containing articles ofmanufacture which are normally subject to corrosion and which have beenrendered substantially non-corrodible by.

treatment with a dispersion of a certain free dicarboxylic acid in asuitable vehicle.

Metallic surfaces, particularly those containing iron, requireprotection against the hazard of corrosion in the presence of water. Toillustrate: Moisture readily attacks finished or semifinished metalobjects unless the metal surface is covered during storage or shipmentby a protective coating such as a, slushing oil; water in Diesel enginefuels often corrodes closely fitted parts such as are found in Dieselengine unit type injectors; water in turbines corrodes turbineApplication February 8, 1943', Serial No. 475,204

17 Claims.

although lower or higher temperatures may be employed. The lowertemperature limit is usually determined by the solidificationtemperature of the liquid, and temperatures should'be below the boilingtemperature of the vehicle and below the decomposition temperatures ofboth the vehicle and the dicarboxylic acid.

Metals capable of being thus protected are in particular the ferrousmetals, e. g., soft iron, various steels, cast iron, and to a lesserextent copper, brass, bronze, zinc, aluminum, magnesium alloys, variousbearing metals as copperlubricant circulatory systems, particularly thegovernor mechanismsoi steam turbines; and-water in hydrocarbon oils,such as gasoline, rusts steel storage tanks and drums; water inantifreeze compositions causes corrosion in automobile radiators, etc.Corrosion not only has a deleterious effect upon the metal surfaces, butalso frequently loosens finely divided metal oxides which may act asoxidation catalysts increasing the rate of deterioration of variousorganic compounds with which they come in contact or may enter betweenmovingparts of machinery where they act as abrasives.

It is a purpose of this invention to treat metals or articles ofmanufacture containing metals in a way so that they become resistant totheir normal corrosion. It is a specific purpose to treat in a simplemanner accurately machined metal parts so that they may be handledwithout developing corrosion, particularly in places where fingerprintshave been left, Another purpose is to protect iron or "steel equipmentexposed to the atmosphere so that its rusting is prevented or at leastretarded. Still another purpose is to protect mechanical equipment fromrusting,

' which equipment stands idle and/or is shi ped over long distances. Wehave discovered that structural metals which are used in theconstruction of various articles of manufacture and are subject. to anormal corrosion can be protected simply and eifectively by treatingthem with a line dispersion.qf a dicarboxylic acid having at least 16carbon atoms and a. linkage comprising one or ous to recite.

lead, cadmium-nickel, silver-nickel, etc.

Articles containing these metals are too numer- However, it may bementioned that the problem of rust prevention is critical, for example,where accurately machined parts are involved, such as piston rings,engine cylin ders, bearing shafts, plungers of pumps, etc. In

other instances, rust prevention may perhaps not be critical, but ofvast economic importance as, for example, in the mass production ofsteel castings which are piled up and often set inthe open for monthsbefore being finished.

Corrosion may be due not only to atmospheric exposure, but may be causedor accelerated by contact with acidic materials, for example, bytouching with the fingers. It also may occur in closed systems, as-ininternal combustion-engines, steam turbines, pipe lines, etc., due tothe corrosive influence of various impurities as water, oxygen, CO2,salts, inorganic or organic acids, etc. The treatment, according to thisinvention, for

" the prevention of corrosion may consist of a single contact of themetal to be protected with the dispersion containing the dicarboxylicacid, or may comprise repeated contacts effected at intervals, or mayconsist of a continuous treatment lasting as long as the use of theparticular dispersion or piece of equipment or both. The choice of anyparticular type of these treatments is usually dictated bycircumstances. For example, if newly machined and finished .machineparts are to be rust-prooied, they may be dipped or sprayed with asuitable dispersion, and then stored away. On the other hand, if rustprevention in a steam turbine is desired, it is preferable that thecirculating lubricating oil contain the active rust-preventive compoundand more elements selected from the group consisting of sulfur, seleniumand tellurium.

The dispersion may be a true or colloidal solution in a suitable vehiclewhich is capable of flowing under the conditions of the treatment, i.e., is liquid or plastic at the temperature of The treatment.

atmospheric if the vehicle is normally liquid,

contact is made as long as this oil is used. Should, after a while, thisoil be discarded and be replaced by another one not containing arust-preventive, then corrosion protection usually lasts for a long timethereafter, due to the protective film left-behind. In cases where thisfilm is mechanically destroyed, as in bearings or gears, etc., runningunder extreme loads, the protective film must be renewed continuously;otherwise rust protection fails.

The general formula. of the corrosion-preventive acids of this inventionis: ci o on eke-o 0 0 H wherein X, is sulfur,'selenium or tellurium, and

u, v and w are integers, preferably 1 or 2, although 11. and u may befrom 1 to about 10. The unoccupied valences are tied to the same ordifferent hydrogen or hydrocarbon radicals, the latter of which may bealiphatic, cycloaliphatio, aromatic or mixed and may-containsubstitution radicals which are not too strongly polar, such as halogen,etc., but should preferably be free from strong polar radicals,sucha's"0H, =CO,

H NH2, SH, etc.

The above formula may take the following form:

o wn'o awooon As indicated before, the acid should have a total numberof carbon atoms not less than 16, and preferably between about 20 and 60for good anti-corrosive properties. Both true solutions and colloidaldispersions in various vehicles are effective in the matter of corrosionprotection. However, true solutions are preferred for two reasons:first, colloidal solutions may under some circumstances coagulate, inwhich case at least a portion of the active protective agent iseliminated; and second, colloids tend to cause emul-. sification of oilyvehicles with water, which in many instances, such as in the lubricationof steam turbines, is undesirable.

It is, of course, desirable that the acids be relatively resistant tooxidation, and therefore they should not contain more than one aliphaticdouble bond per hydrocarbon radical and preferably none.

Generally, in the presence of copp r, acids containing a link of a.single X atom (X being S, Se

or Te) seem to impart to oils longer induction periods than acids havingXX linkage, while the latter impart lower rates of oxygen absorptionafter the induction period. Thus disulfide, diselenide or ditellurideacids may be preferred for some oils, while acids with mono linkages maybe better for other oils. Polysulflde linkages of more than two sulfuratoms may also be 'used. They are, however, believed to contain only twosulfur atoms in the normal chain between the carboxyl radicals, theremaining sulfur being attached in the form of a branch, such as s s i ietc. If-desired, the carboxyl radicals may be linked through a sulfurradical s o o I The closeness of the sulfur, selenium or tellurium tothe carboxyl radical has some bearing on the corrosion-protectiveproperties of the acids. In general, the closer they are, the morepotent the compound is, other things being equal. Thus,

from this angle, acids in which the sulfur, selenium or tellurium atomsare in alpha or beta position to at least one, and preferably bothcarboxyl radicals are the best anti-corrosives.

Accordingly, among the groups of acids are several which areparticularly useful. For example, di-fatty acid alpha sulfides,selenides and tellurides having the formula m-on-coon m-tn-coon whereino is 1 or 2, and R1 and Rs are alkyl radicals whose total number ofcarbon atoms is not less than 16 (one of them may be hydrogen). Ifdesired, R1 and R2 may comprise alicyclic rings, in which case one orboth of the car-boxylic acids are naphthenic acids; or else R1 and R2may con-.

@mn-wn-ooou (BOOK OOH 00H wherein Rl-R3 are hydrogen or hydrocarbonradicals, the latter preferably being aliphatic although they maycomprise cycloaliphatic or aromatic groups. The unoccupied'valences aretied to hydrogen or hydrocarbon radicals, which radicals may be the sameor different in different groups. X again is sulfur, selenium ortellurium;

- n is an integer of 1 up to about 8, and preferably 1 or 2; .and o is 1or preferably 2. The total number of carbon atoms is preferably 20 ormore.

The dicarboxylic acids of this invention may be produced in severalways. One convenient method comprises reacting a chlorinated fatty acidor other suitable monocarboxylic. acid with an a.lkali metal sulfide orpolysulfide. Commer-v cially available alkali metal sulfides are usuallymixtures containing mono-, diand sometimes higher polysulfides.Therefore this reaction may be utilized to produce mixtures of differentsulfide dicarboxylic acids. Such mixtures are very excellent for thepurpose of this invention, sincev they are usually more soluble invarious vehicles and as-oxidation stable as the best of the pureindividual compounds.

Disulfides maybe produced by first preparing a hydrosulfide derivativeof a fatty acid or other suitable carboxylic acid by reaction of achlorinated carboxylic acid with NaHS, KHS, etc., then oxidizing thehydrosulflde to the .disulfide.

Higher 'polysulfldes may be obtained by oxidiz-. ing with sulfur in thepresence of lead oxide.

Asymmetric dicarboxylic acids may be produced, for example, by reactinga suitable chlorinated monocarboxylic acid with an alkali meta1 salt ofthioglycolic acid or of a fatty or other suitable monocarboxylic acidhydrosulfide.

Suitable monocarboxylic acids for the production of our dicarboxylicacids include fatty acids,

such as acetic acid, propionic, butyric, isobutyric valeric, caproic,caprylic, decylic, undecylic, lauric, myristic, palmitic, stearic,arachic, behenic, oleic, phenyl acetic, phenyl propionic, phenylstearic, tolyl stearic, naphthyl acetic, naphthol stearic, acids, etc.Naphthenic acids, such as are obtained by caustic alkali extraction ofrelatively high-boiling straight-run petroleum oils, such as kerosene,gas oil, lubricating oils, etc., may be used; or synthetic naphthenicacids, such as cyclohexyl acetic, cyclohexyl propionic, cyclohexylstearic acids, corresponding alkyl cyclohexyl, tetrallyl, dicyclohexylfatty acids, or acids derived from naphthenes obtained by hydrogenationof isophorone, diisophorone and homologues, etc. In choosing amonocarboxylic acid from the list for use in a certainreaction, sightmust not be lost of the fact that the dicarboxylic acid must have aminimum of 16 carbon atoms.

The vehicles to which dicarboxylic acids of this invention may be addedfor the purpose of producing corrosion-protective compositions may bedivided into several groups. 'In the first place, they may be liquids orplastics, the only requirements as to their physical state being '(inaddition to their being able to act as carrier for the acids undernormal atmospheric conditions) that they be spreadable over metalsurfaces. Spreading may be accomplished by immersing, flooding,spraying, brushing, trowelling, etc.

After being applied, all or part of the vehicle butyl ethers; neutralesters of carboxylic and other acids as ethyl, propyl, butyl, amyl,phenyl, cresyl and higher acetates, propionates, butyrates, lactates,laurates, myristates, palmitates, stearates, oleates, ricinoleates,pthalates, phosphates, phosphites, thiophosphates, carbonates;

natural waxes as carnauba wax, candelilla wax,

distillates, kerosene, gas oil, lubricating oils may be evaporated, orit may bemore or less permanent. In other words, both volatile cariersmay be used, or substances which do not materially volatilize undernormal atmospheric conditions. As to chemical requirements, the vehiclemust be stable under ordinary conditions of storage and use and be inertto the active inhibitors.

Thus the vehicle should preferably be substantially neutral, although itmay be weakly acidic or basic, preferably having dissociation constantsnot above about 10 In vehicles of low dielec-. tric constant, ashydrocarbon oils, which are not conducive to ionization of dissolvedelectrolytes, relatively small amounts, i. e., about .1% to 5% ofvarious carboxylic acids, such as fatty or naphthenic acids, may bepresent, and in many instances this may even be beneficial.

Both polar and non-polar vehicles may be employed. Among the former arewater, alcohols,

such as methyl, ethyl, propyl, isopropyl, butyl,

amyl, hexyl, cyclohexyl, heptyl, methyl cyclohexyl, octyl, decyl,lauryl, myristyl, cetyl, stearyl, benzyl, etc., alcohols; polyhydricalcohols as ethylene glycol, propylene glycol, butylene glycol,glycerol, methyl glycerol, etc.; phenol and various alkyl phenols;ketones as acetone, methyl ethyl ketone, diethyl ketone, methyl propyl,methyl butyl, dipropyl ketones, cyclohexanone and higher ketones; ketoalcohols as benzoin, ethers as diethyl ether, diisopropyl ether,diethylene dioxide, beta-beta dichlor diethyl ether, diphenyl oxide,chlorinated diphenyl oxide, diethylene glycol, triethylene glycol,ethylene glycol m'onomethyl ether, corresponding ethyl, propyl,

(which may be soap-thickened to form greases), petrolatum, parafiin wax,albino asphalt, carbon tetrachloride, ethylene dichloride, propylchloride, butyl chloride, chlor benzol, chlorinated kerosene,chlorinated paraffin wax, etc.

The amounts of the dicarboxylic acids which must be incorporated in theabove vehicles to produce .corrosion-protective compositions varyconsiderably with the type of vehicle used. As a general rule, thepresence of resinous materials, particularly those of a colloidalnature, calls for relatively larger amountsof inhibitors. Resinousmaterials which interfere with the activity of the inhibitors compriseasphaltenespetroleum resins, various other natural resins, as rosin,resins formed by polymerization of drying fatty oils, phenol-formaldhyderesins, glyptal type resins formed by esterification of polyhydricalcohols with polycarboxylic acids, etc.

In the absence of such resinous materials, amounts required of thedicarboxylic acids vary from about .00l% up to about .l%, althoughlarger amounts may be used. However, where the acids are in colloidaldispersion, rather than in true solution, a concentration in excessofabout .l% may result in relatively quick loss of part of the inhibitorby precipitation and settling.

In. the presence of resins and other colloid amounts in excess f l. andup to 5% may be required. Inasmuch as resins may act as protectivecolloids, compositions containing these large amounts of colloidallydispersed inhibitors, together with resin, may be quite resistant toprecipitation and settling.

Since resinous and gummy substances in the vehicles do call for greateramounts of inhibitors, it is usually desirable to refine normally liquidvehicles thoroughly and free them from gummy substances, therebyimparting to them maximum inhibitor susceptibility. This is ofparticular importance, for example, in lubricating oils, specificallysteam turbine oils, which are advantage ously highly refined before theinhibitor is introduced. Suitable refining treatments include, forexample, extraction with selective solvent for aromatic hydrocarbons asliquid S02, phenol, furfural, nitrobenzene, aniline,beta-beta-dichlorine diethyl ether, antimony trichloride, etc.;treatment with AlCla', sulfuric acid, clay, etc.

If the treatment produces a sludge, special care must be taken to removeit very thoroughly and completely.

Example The effectiveness of several dicarboxylic acids of thisinvention in suppressing corrosion was Additive Water Time CorrosionHours 2% NaCl 48 None-perfect pro .0192, alpha alpha di- 7 tection.lauric acid sulfide. Synthetic sea 48 Do.

water.

s thetic sea is Do v atcr. l% alpha alpha di- Synthetic sea 48 Do.

gglmitic acid sulwater. e. .0l% alpha alpha di- 2% N 9.01 48 Do.

stearic acid sulfide.

Do Sea water..." 44 Slight corrosion,

- less than Do Synthetic sea 48 None-perfect prowater. tection. .005%alpha alpha dido a. 25 Slight corrosion,

stearic acid sulfide. less than 10%. .0195 alpha-lauric 8.1- do 48None-periect pro gga-stearic acid sulction.

e. .0i% alpha alpha di- 2% NaCl 48 Perfect.

stearic acid disul- Synthetic sea 24 Very slight corrofide. water. sion..0l% alpha hexadecyl 2% NaCl 24 Do.

thioglycolic acid.

We claim as our invention:

1. A structure normally corrodible metal coated with acorrosion-preventive film of a free dicarboxylic acid having atleast 16carbon atoms, the two acid radicals in said 'acid being linked throughan element selected from the group consisting of S, Se and Te. v v

2. The coated metal of claim 1, the film of which contains an acidhaving between 20 and 60 carbon atoms.

' 3. A structural normally corrodible metal coated with acorrosion-preventive film of a free dicarboxylic acid having at least 16carbon atoms, and having the formula wherein X is an element selectedfrom the group consisting of S, Se and Te, u and v are integers rangingfrom 1 up to about 10, and u is l or 2.

4. A structural normally corrodible metal coated with acorrosion-preventive film of a free dicarboxylic acid having at least 16carbon atoms and the formula wherein R1 and R2 are hydrogen orhydrocarbon radicals, X is an element selected from the group consistingof S, Se, and Te, and o is 1 or 2.

5. A structural normally corrodible metal coated with acorrosion-preventive film of a di(hydrocarbon carboxylic acid) alphaalpha sulfide having at least 20 carbon atoms.

6. A structural normally corrodible metal coated with acorrosion-preventive film of a free difatty acid sulfide having at least20 carbon atoms.

7. A structural normally corrodible metal coated with acorrosion-preventive film of a di-fatty acid monosulfide having at least20 carbon atoms.

' 8. A structural normally corrodible metal coated with acorrosion-preventive film of a di-fatty' acid disulfide containing atleast 20 carbon atoms.

9. A structural normally corrodible metal coated with acorrosion-preventive film of a di-fatty acid alpha-alpha sulfide havingat least20 carbon atoms.

10. A structural normally corrodible metal coated with acorrosion-preventive film of alphaalpha' distearic acid sulfide.

11. A structural normally corrodible metal hicleof a dicarboxylic acidhaving at least 16- carbon atoms, the carboxyl radicals of said acidbeing linked through an element selected from the group consisting. ofS, Se and Te.

15. Method of protecting a normally corrodible structural metal fromcorrosion comprising spreading over its surface a fine dispersion in asubstantially neutral vehicle of a dicarboxylic acid having at least 16carbon atoms to deposit on said metala protective coating of said freeacid, the carboxyl radicals in said acid being linked. through anelement selected from the group consisting of S, Se and Te.

16. The method of protecting a normally corrodible structural metal fromcorrosion comprising spreading over its surface a fine dispersion in asubstantially neutral vehicle of a dicarboxylic acid havingat least 16carbon atoms and having the formula c .-cooir (Iii)- yak-Coon wherein Xis an element selected from the group consisting of S, Se and'Te, u andv are integers ranging from 1 up to about 10, audio is l or 2. 17. Themethod of protecting a normally corrodible structural metal fromcorrosion comprism-cn-coon wherein R1 and R2 are hydrogen or hydrocarbonradicals, X is an element selected from-the group consisting of S, Seand Te, and o is l or 2.

' ERNEST w. ZUBQLIN.

EMME'II' R. BARNUM. arms R. wnrra.

